The traditional way of comparing ballistic evidences such as cartridges and bullets is for a human specialist to manually examine the reference and all the candidates with a comparison microscope. This is a very tedious and time-consuming process that makes matches less likely. Recently, a few systems have been invented to automatically perform ballistic image comparisons. For example, the Russian Condor system (Russian patents No. 2130628, No. 2155378, and No. 2174251), the German GE/2 system (inventors M. Heizmann and F. Puente Leon), the Forensic Expert Assistance System Abal Labview (FEASABLE) system from ABAL in Belgium. These systems were created to speed up the work of firearm examiners whose numbers are few. The common principle behind these systems is the acquisition of images (2D or 3D) from evidence, the extraction of signatures, and the comparison of these signatures, often performed by some kind of cross-correlation. Once a human operator has acquired the reference image, the rest of this process can be done in a matter of hours even for large databases of previously acquired images.
One of the critical parts of this operation is the creation of “good” signatures from the acquired images. This is particularly true of non-pristine bullet images, which are very noisy and contain a lot of random marks that are not relevant to the matching operation. These random marks are consciously ignored by a firearm examiner during his visual exam but can seriously compromise the performance of an automated system. To solve this problem, certain systems, such as FEASABLE, ask the user to manually draw the contour of the regions relevant to the matching step over the original reference image. These regions then contain mostly lines that share the same orientation and of course excludes parts of the image that do not contain lines.
The selected regions alone are then considered for the creation of signatures. Using only the regions determined by the expert dramatically improves the results of the matching process.
The drawback of this approach is that it takes the knowledge and training of a firearm examiner to select the right regions that will be used for the creation of the signatures. As the number of these experts is much smaller than the number of potential users of the system, this specialized knowledge cannot be expected from the average user.